Carrier Aggregation will be used in future LTE networks to provide improved data rates to users. Carrier aggregation consists of transmitting data to or receiving data from the UE on multiple carrier frequencies (“component carriers”). The wider bandwidth enables higher data rates. Thus the UE can be configured, for communication, with multiple component carriers. Here communication involves transmission and/or reception of data and signaling. Some of these component carriers may be “activated”. If a component carrier is activated, it can be used for data transmission to the UE. Configured component carriers are candidates for activation; that is, based on the arrival of a significant amount of data, one or more of the configured component carriers can be activated.
The UE is required to perform various radio resource management measurements to support component carrier (CC) management and to support mobility during carrier aggregation operation. CC management can include addition of CCs to, removal of CCs from and replacement of CCs in the configured CC set. Mobility can include handovers of the UE between eNBs, between sectors of an eNB, between remote radio heads connected to the same eNB and between repeaters of the same eNB. Such measurements can be a significant drain of the UE battery—particularly because with carrier aggregation, the UE would be performing measurements of more frequencies that if carrier aggregation were not used. The present disclosure concerns the measurements performed on the component carriers and tries to minimize them.
In LTE Release 8, a parameter called “s-Measure” can be defined by the network. The s-Measure indicates a signal strength or signal quality level. If the UE finds the signal of the serving cell to be below the s-Measure, it performs measurements of other frequencies (i.e., frequencies other than the serving frequencies) and other radio access technologies (such as UMTS and GSM). If the UE finds the signal of the serving cell to be above the s-Measure it can avoid performing measurements (the rationale being that if the serving cell measurements are high, then there is no immediate need to handover the UE to another cell, and therefore no need for measurements and measurement reports). Thus, the s-Measure enables significant battery savings for the UE.
With Carrier aggregation, a UE can be configured with multiple carriers from the same eNB. Thus the UE can have multiple serving cells, each serving cell operating on a different carrier. One of these serving cells is designated as the P-cell (the corresponding downlink CC is referred to as the primary component carrier or PCC) and the other serving cells are designated as the S-cells (the corresponding downlink CCs are referred to as the secondary component carriers or SCCs).
It is possible to use the s-Measure parameter provided by the P-cell to control all measurements; that is, the UE uses the P-cell as the reference for the s-Measure and it can avoid all measurements (including measurements of cells on SCCs) when the P-cell signal is above the s-Measure. However, this results in not being able to effectively perform CC management decisions—i.e., without measurements on SCCs, the network cannot determine when to add/remove/replace CCs.
The various aspects, features and advantages of the invention will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description thereof with the accompanying drawings described below. The drawings may have been simplified for clarity and are not necessarily drawn to scale.